


The Rate-Limiting Step

by Aerlalaith



Category: Supernatural
Genre: Alternate Universe, Alternate Universe - Academia, Alternate Universe - College/University, Astronomy, Domestic Fluff, Fluff, Geology, M/M, Nerd Castiel, Nerd Dean Winchester, Outer Space, Science Boyfriends
Language: English
Status: In-Progress
Published: 2018-11-25
Updated: 2018-11-25
Packaged: 2019-08-29 11:33:57
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,551
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16743208
Author URL: https://archiveofourown.org/users/Aerlalaith/pseuds/Aerlalaith
Summary: Collection of loosely connected one-shots detailing the domestic adventures of nerdy geologist/astronomer Dean and Castiel.





	The Rate-Limiting Step

**Author's Note:**

> Casthewise on Tumblr stated a need for Geologist/Astronomer nerdy boyfriends Dean and Castiel. I do these science things in real life sometimes so, here we are.
> 
> I have the idea for a couple of one shots, all related, but no cohesive story, so they'll be posted here as they get written, but each one basically stands alone. The rating might go up.

“Units!” said Dean. “Goddamn fucking—no, listen. Listen to me, Sammy.”  He readjusted his cell phone at his ear, then caught the very top of a sheaf of papers threatening to fall from his arms as he stalked down the hallway. “Last semester I had a kid literally—no, fucking _literally_ —I get this goddamn email all like ‘so we’re using units of meters cubed for transmissivity, right? Right?”  
   
A few visitors to the department museum looked up from the glass mineral cases to eyeball him as he swept past. An elderly woman shook her head, then turned back to the malachite.  
   
“And I’m all like— _no_ , the units are not fucking—they’ve been length squared per time this whole fucking semester, why the fuck would they suddenly be cubed—ah, shit.”  
   
The was a thump, the clatter of a phone crashing to the ground, and then nothing. The silence on the other end of the line lasted long enough for Sam to prompt, “Dean? Dean?”  
   
“Shit, my bad,” Dean was saying, as he tried to help drag the guy he’d just unwittingly barreled into, off the floor.  
   
“Maybe you should watch where you’re going next time,” the guy growled as he shook off Dean’s hand and got to his feet. He brushed museum dust off of black slacks, then lifted his head to glare at Dean.  
   
Very unfortunately, the lighting in the museum happened to play off the guy’s cheekbones and the bright blue of his eyes in a way that made Dean’s mouth go dry very, very suddenly, so there was about a five second delay while Dean’s brain waited to process basic English. Dean, naturally, spent those five seconds staring unabashedly at the dude’s mouth, and thinking, _fuck_.  
   
Then his words penetrated. Dean flushed. “Hey, man. I said I was sorry.”  
   
The guy narrowed his eyes at him. Dean squared his shoulders. Maybe the museum wasn’t the best place for it, but that didn’t mean Dean wasn’t ready to throw down. Yeah, okay, so he’d knocked the guy on his ass, but it hadn’t been on purpose. Dude didn’t need to be such a dick about it.  
   
“Hey, Cassie. Cassie!”  
   
They both started. From the other side of the museum, another guy stood waving. “I’ve been looking all over for you—I finally found the bloody room. Swear to god though, one of the tray of rocks was labeled ‘asbestos’ so that’s a year of our lives just siphoned away from sitting in there I expect. Hello, who the hell are you?”  
   
This last was directed at Dean, who took in the partly unbuttoned v-neck, blond hair, and sharp nose with something approaching disdain. Edging towards the pile of papers he’d dropped on the floor when he’d, obviously mistakenly, tried to help the first guy up, he opened his mouth to speak, but—  
   
“Never mind,” said— _Cassie_? What the actual fuck? Dean’s luck couldn’t be that bad. It couldn’t. “We’re going to be late.”  
   
“We have ten minutes before the class starts,” V-neck clucked.  
   
Considering where Dean also intended to be in the next ten minutes, this seemed like a bad sign. But then, Dean reminded himself, in two years he’d never seen these yokels in his life, so why the fuck would they be in a graduate level geo class with him?  
   
Must be some other class.  
   
“Okay, well,” said Dean, now one hundred percent invested in getting the fuck out of there, no matter how nicely _Cassie’s_ shirt stretched across his shoulders. Dean had a strict no-jerk and no ‘ _Cassie´_ policy these days. “Sorry about—the thing. I’ll get out of your way.”  
   
And with a quick swoop to the ground to collect his pile of papers and the cell phone that was still—shit—still connected to Sam, Dean was heading off to his office so that he could dump all of his shit on his desk and not be late to _his_ class, which was absolutely definitely not _their_ class.  
   
“Who was that?” Dean heard the second guy say, as the museum receded behind him.  
   
“Never mind,” _Cassie_ grunted again. “You said you found the room? Where is it?”  
   
   
#  
   
   
It was their class.  
   
Dean stared numbly at the syllabus in front of him:  
              
_ASTR/GEOL 5800_  
_PLANETARY SURFACES AND INTERIORS_  
   
“Why are you even taking this class?” said Jo, sliding into the seat next to him. “You don’t need the credit.”  
   
Cassie and his friend hadn’t even bothered to glance over at him. Some very tiny, monkey part of Dean’s brain took note of the fact that Cassie’s dark hair was just as messy as his clothes were neat.  
   
“Dean!” Jo snapped.  
   
He shook himself. “What?”  
   
She repeated the question. He shrugged, pointing to himself. “I’m a geologist. This is a geology class.”  
   
“You’re not a planetary geologist,” said Jo, with all the authority of someone who spent hours cutting tiny holes into priceless meteorites and then shooting them with lasers. “This has nothing to do with your research.”  
   
“Earth is a planet.”  
   
“Your face is a—”  
   
“Did you know this was cross-listed with astronomy?” Dean blurted out, then felt the back of his neck redden. Jo stared at him like he was an idiot.  
   
“Yeah,” she said slowly. “A lot of them are.”  
   
“Oh,” said Dean, and very deliberately did not look over at Cassie and his friend as the lecture started in earnest.  
   
It had been a while since he’d thought about planets other than the one he was presently on, Dean admitted later, over his coffee and one of the three papers he was supposed to be reading. He liked the café because it was tucked away from where the main swarms of undergrads funnelled through the building, and rarely got too crowded. Today though, there must have been something going on, or maybe it was just the start of the semester, but almost every seat was taken.  
   
He wasn’t too surprised, therefore, to hear a voice say, “Do you mind if I sit here?” to which Dean responded with an automatic,  
   
“Go for it.” And it was only after his mouth had said this, that he even bothered to look up and see who’d asked.  
   
Blue eyes blinked back at him.  
   
“Thank you,” said Cassie, as he sat down at Dean’s table.  
   
“Uh,” said Dean, very eloquently. Cassie was wearing what was hopefully a different white button down than the day before, and the same tan trench coat. There were dark circles under his eyes, and he clutched his cup of coffee like a lifeline. Comparatively, Dean in his plaid and field jeans felt kind of underdressed.   
   
“I heard you tell Joanna Beth you were a geologist,” Dude started, apropos of nothing. Dean gaped at him.  
   
“Um?” said Dean, after another moment of the guy looking at hum expectantly. “Yeah—I mean, you know Jo?”  
   
“We’ve had classes together before.” He squinted at Dean, then stuck out his hand. “I apologize for being rude yesterday. I was…” he hesitated. “Stressed.”  
   
“Um,” said Dean. “No, that’s. That’s cool, man. “I, uh.” He took the hand gingerly. “Dean.”  
   
“Castiel.”  
   
“Not Cassie?” Dean said, before his brain could catch up with his mouth and beat it into submission. Cas— _Castiel_ sighed.  
   
“Only to Balthazar,” he grumbled.  
   
It was, oddly enough, the irritation in his voice that pushed Dean over the wavering edge into forgiveness. Dean had those kind of friends. Hell, Dean _was_ that kind of friend.  
   
“Cool,” Dean said. “How about I just call you Cas?”  
   
Cas tilted his head. “Why?” He was favored with a winsome smile, that kind that Dean usually only pulled out in bars or on his adviser when he was telling her about just how long he planned to be gone over Christmas.  
   
“It’s shorter.”  
   
“I see.” From his expression. Cas clearly did not see. He fiddled with the lid on his coffee cup.  
   
“Jo’s a geologist too,” Dean said, watching his face.  
   
“Yes.”  
   
“So…what?” Dean flashed him a small grin. “Looking to defect from the Astro department? Need some advice?”  
   
Cas just looked even more confused. “No,” he said slowly. “I—” he caught himself, looked down at the table, drummed his fingers, and then back up at Dean. “I’m looking for papers on surface processes in extreme environments. Low temperature aqueous geochemistry. Joanna Beth said you were the one to ask.”  
   
Dean’s eyebrows shot up. “Oh,” he said, now returned to his previous levels of eloquence. “I mean.” Cas was watching him patiently. Dean swallowed. “I mean, yeah. That’s kind of—kind of what I do.”  
   
Cas nodded as if satisfied, and took a long sip of his coffee. Dean tried to avoid looking at his throat as he swallowed. “You’re a master’s student?”  
   
“Nah,” said Dean. “I mean. I was.” He leaned back in his chair, waved his hand at the general building around them. “I switched over to do a PhD. Last year.” His nose wrinkled. “Found a cool topic and was like…” he trailed off, shrugging. “You know.”  
   
He caught eyes with Cas who, for the first time since their meeting, looked understanding. The corner of his mouth twitched up. “Yes,” he said.  
   
Dean stared. Then, he realized he was staring. He coughed. “So,” he said. “Um, papers?”  
   
“Yes, please.” Cas sat up straighter. “I don’t have much of a geology background, and I’m finding that understanding surficial processes are becoming crucial to my research.”  
   
“That’s why you’re taking the class?”  
   
Cas nodded. “I don’t need any more credits,” he admitted. “But I thought it might be useful. However, looking at the syllabus from yesterday, it seems we’re going to be spending the majority of the semester on the internal processes—”  
   
“They are, technically, connected,” Dean said, kind of just to be a dick. Cas flushed.  
   
“Yes, I’m aware. However, if we’re discussing the interaction between icy surfaces and the atmospheres of terrestrial planets and moons—”  
   
“What, Mars? Shitty excuse for an atmosphere.” He got a glare for that one.  
   
“It _is_ an atmosphere.”  
   
“Never said it wasn’t. Just saying it’s a shitty one.”  
   
“I’m not just looking at Mars.” Cas folded his arms. “Do you have papers to recommend to me or not?”  
   
“Yeah, sure. Just Earth stuff though.” Dean cracked open his laptop. He had printed out the papers he’d planned to read at the coffee shop, just because of the headache he knew he’d get if he stared at his screen too long, but like a security blanket, he’d brought his laptop along too, just in case. “I’m not really a planetary guy.”  
   
“I believe Earth is technically a planet,” Cas said offhandedly, and Dean’s head shot up so fast he nearly cricked his neck.  
   
“Dude,” he said. _“Dude_.”  
   
Cas frowned. “What?”  
   
Smiling a little, shaking his head, Dean just swivelled around his laptop so the screen was facing Cas. He gestured at the screen. “I’ve got ‘em all on Mendeley. Go nuts.”  
   
Cas’s eyes widened as he took in the computer screen, hand hovering over the trackpad. “Really?”  
   
“Yeah, sure.” Dean pushed it over to him. “Just tell me which ones you want. I’ll email them to you. Or dropbox if it’s a lot. You know. Whatever.”  
   
“Thank you,” said Cas softly, eyes already scanning the screen. “That’s really—you could just send me a couple.”  
   
“Nah,” said Dean. “I’d probably pick the wrong ones, anyway.” He toyed with his coffee cup. “I’ll need your email though.”  
   
“Of course,” said Cas, clearly distracted. “Is the Hayes et al. paper good? I think I saw him on the syllabus…”  
   
“He does a good review, I think.” Dean pursed his lips. “Twenty-fourteen—no, twenty-fifteen. Uh…”  
   
“Yes, okay,” Cas murmured. “I see it. Can I just highlight the ones I want?”  
   
“Makes sense.”  
   
“And I’ll give you my email.”  
   
“Cool.”  
   
“And my number.”  
   
“Yeah—what?” Dean definitely did not squeak.  
   
“My number,” Cas repeated. His gaze flickered to Dean, and for a second Dean could’ve sworn that Cas was _looking him over_ , but then the feeling was gone, and it was just one tired, coffee-fueled grad student eyeing another tired, coffee-fueled grad student, computer full of research papers between them. “In case I have questions.”  
   
“Uh, yeah. Okay,” said Dean. That made sense. That made a lot of sense. Unfortunately. “Let me just—” he fumbled with his phone, then pushed it out towards Cas. “Here.” Cas took it, typed something in, then handed it back.  
   
“Send me a text?”  
   
“Sure,” Dean muttered. He pressed the contact for _Castiel Novak_ and sent a quick, _hey, it’s Dean._  
   
Something in Cas’s pocket pinged, and Cas reached around to pull out his own phone. “Thank you,” he said. “Oh.” His eyebrows drew together. “What’s your last name?”  
   
“My—oh.” Dean nodded like an idiot. “Yeah, sorry, man. It’s Winchester.”  
   
“Winchester,” Cas said slowly, typing it out. “All right.”  
   
“You got a lot of Deans in there to keep track of or something?” Dean asked lamely. Cas fixed him with a look.  
   
“No,” he said, “Just you.”  
   
Bearing the full brunt of Cas’s very focused gaze, it was the best Dean could do to keep himself from turning red or swallowing very loudly. Damn, it was like being under one of Jo’s lasers. “Oh,” he managed, and breathed a small sigh of relief when Cas returned to perusing his Mendeley for articles.  
   
“All right,” Cas said, a few minutes later. Dean was grateful. He could only pretend to keep sipping an empty coffee cup and reading an article on mantle fluid dynamics that held just about zero interest for him, for so long. “I’ve picked the ones I think I could start with.” He turned the laptop back around towards Dean, then stood, pushing his chair back with a scrape across the floor. “You don’t mind sending them to me?”  
   
“No, it’s cool. I’ll send them ASAP.” He hands were already pulling the laptop back towards his side of the table.  
   
Cas’s eyes met and held his. “Thank you,” he said again, sincerely.  
   
Despite himself, Dean could feel his cheeks heat. He ducked his head. “No problem, dude,” he said. “Seriously.”  
   
Of course, Cas held out his fucking hand. “It was nice to meet you, Dean Winchester,” he said solemnly. Against his better judgement, Dean took it. He might have expected Cas’s hands to be soft, wasn’t like the guy did fieldwork or anything, but there were callouses there, and his grip was warm and firm.  
   
“Yeah,” said Dean, like an idiot. “See you around.”  
   
Cas nodded, eyes flickering briefly to Dean’s laptop, then back at Dean, and then in a whirl of trench coat, he was out of the coffee shop, and swept up in a throng of chatting, shouting undergrads. Unable to help himself, Dean stared after his vanishing form.  He exhaled, then jumped when his phone buzzed on the table. He glanced over at the screen.  
   
Castiel Novak _: Hello. It’s ‘Cas.’_  
   
Jesus Christ, thought Dean, laughter bubbling up in his throat. He’d actually used quotations around his own name.  
   
Castiel Novak _: Thank you for your help today._  
   
Dean Winchester: _No prob, dude_  
   
Castiel Novak: …  
   
Castiel Novak: …  
   
Castiel Novak: _Mars has a very interesting atmosphere._  
   
Dean shook his head, warmth from bemusement and something else, unknown, pooling in his stomach.  
   
_What a nerd._

 

 


End file.
